Ascp FAQs

How do I control the transfer speed?

You can specify a transfer policy that determines how a FASP transfer utilizes the network
resource, and you can specify target and minimum transfer rates where
applicable. In an ascp command, use the following flags to
specify transfer policies that are fixed, fair, high, or low:

Policy

Command template

Fixed

--policy=fixed -l target_rate

Fair

--policy=fair -l target_rate -m min_rate

High

--policy=high -l target_rate -m min_rate

Low

--policy=low -l target_rate -m min_rate

The policies have the following characteristics:

fixed

Attempt to transfer at the specified target rate, regardless
of network capacity. Content is transferred at a constant
rate and the transfer finishes in a guaranteed time. The
fixed policy can consume most of the network's
bandwidth and is not recommended for most types of file
transfers. It requires setting a maximum (target) rate
(-l option).

high

Adjust the transfer rate to fully utilize the available
bandwidth up to the maximum rate. When congestion occurs,
the transfer rate is twice as fast as a fair-policy
transfer. The high policy requires the setting of
maximum (target) and minimum transfer rates
(-l and -m).

fair

Adjust the transfer rate to fully utilize the available
bandwidth up to the maximum rate. When congestion occurs,
bandwidth is shared fairly by transferring at an even rate.
The fair policy requires the setting of maximum
(target) and minimum transfer rates (-l
and -m).

low

Adjust the transfer rate to use the available bandwidth up
to the maximum rate. Similar to fair mode, but less
aggressive when sharing bandwidth with other network
traffic. When congestion occurs, the transfer rate is
reduced to the minimum rate until other traffic
decreases.

What transfer speed should I expect? How do I know if something is "wrong"
with the speed?

Aspera's FASP transport has no theoretical throughput limit. Other than the
network capacity, the transfer speed may be limited by rate settings and
resources of the computers. To verify that your system's FASP transfer can
fulfill the maximum bandwidth capacity, prepare a client machine to connect to
this computer, and test the maximum bandwidth.

Note: This test typically occupies
most of a network's bandwidth. Aspera recommends this test be performed on a
dedicated file transfer line or during a time of low network activity.

On the client machine, start a transfer with fixed bandwidth
policy. Start with a lower transfer rate and gradually increase the transfer
rate toward the network bandwidth (for example, 1 MB, 5 MB, 10 MB, and so
on). Monitor the transfer rate; at its maximum, it should be slighly below
your available
bandwidth:

$ ascp -l 1m source-file destination

To
improve the transfer speed, also consider upgrading the following hardware
components:

How do I ensure that if the transfer is interrupted or fails to finish, it
will resume without retransferring the files?

Use the -k flag to enable resume, and specify a resume rule:

-k 0 – Always retransfer the entire file.

-k 1 – Compare file attributes and resume if they match, and
retransfer if they do not.

-k 2 – Compare file attributes and the sparse file checksums;
resume if they match, and retransfer if they do not.

-k 3 – Compare file attributes and the full file checksums; resume
if they match, and retransfer if they do not.

Corruption or deletion of the .asp-meta file
associated with an incomplete transfer will often result in a permanently
unusable destination file even if the file transfer resumed and successfully
transferred.

How does Aspera handle symbolic links?

The ascp command skips symbolic links by default.

Important: On Windows, the only option is
skip.

What are my choices for overwriting files on the destination
computer?

In ascp, you can specify the
--overwrite=method rule with the
following method options:

never

Never overwrite the file. However, if the parent folder is
not empty, its access, modify, and change times may still be
updated.

always

Always overwrite the file.

diff

Overwrite the file if different from the source. If a
complete file at the destination is the same as a file on
the source, it is not overwritten. Partial files are
overwritten or resumed depending on the resume policy.

diff+older

Overwrite the file if older and also different than the source. For example, if the
destination file is the same as the source, but with a
different timestamp, it will not be overwritten. Plus, if
the destination file is different than the source, but
newer, it will not be overwritten.

older

Overwrite the file if its timestamp is older than the source
timestamp.

Interaction with resume policy (-k): If
the overwrite method is diff or diff+older, difference
is determined by the resume policy (-k {0|1|2|3}). If
-k 0 or no -k is specified,
the source and destination files are always considered different and the
destination file is always overwritten. If -k 1, the
source and destination files are compared based on file attributes
(currently file size). If -k 2, the source and
destination files are compared based on sparse checksums. If -k
3, the source and destination files are compared based on
full checksums.